Dear Harry and Marlo,
Harry: Thanks for setting the genus-name priority straight. Please remember that the results by Lee and Ó Foighil were incidental, given that the species of Geukensia and Ischadium were used in their study only as outgroups. (Outgroup analysis is a technique traditionally used in phylogenetic systematics that helps determine which characters, in this case gene sequences, are more primitive or more derived in the study group; the outgroup acts as a kind of gauge against which characters of the taxa actually in study are compared).
In their study of Brachidontes, Lee and Ó Foighil picked up two Geukensia and one Ischadium as outgroups, only to get serendipitously to the results under discussion in this thread. To get a more comprehensive picture of the possible relationships among the species of “Geukensia” and “Ischadium,” one would have to bring a larger pool of species assigned to both nominal genera (and other closely related genera) into the analysis.
Sorry for not using italics throughout this message, but for some strange reason I can only send plain text messages to Conch-L (Marlo, your pictures are absolutely outstanding.)
Cheers,
José
________________________________________________________
José H. Leal, Ph.D., Director and Curator
The Bailey-Matthews Shell Museum
Editor, The Nautilus
www.shellmuseum.org
3075 Sanibel-Captiva Road
Sanibel, FL 33957 USA
(239)395-2233
fax (239)395-6706
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From: Conchologists List [mailto:[log in to unmask]] On Behalf Of Harry G. Lee
Sent: Friday, October 09, 2009 7:10 AM
To: [log in to unmask]
Subject: Re: [CONCH-L] Geukensia and Ischadium recurvum (Rafinesque, 1820)
Dear Marlo,
Excellent exposition.
José wrote: "I recall Diarmaid pointing the results to me and commenting on the strange relationship among these species and how I. recurvum would actually be a Geukensia." I think Diarmaid probably meant to say the spp. assigned to Geukensia Poel, 1959 [Type species Mytilus demissus Dillwyn, 1817 by original designation] would be members of Ischadium Jukes-Browne, 1905 [Type species Mytilus hammatus Say, 1822 (= M. recurvus Rafinesque, 1820) by original designation].
The above hypothetical revision leads to an even greater unravelling of mytilid systematics as many authorities have placed Ischadium [Mytilinae] and Geukensia [Modiolinae] in separate subfamilies. Talk about a fly in the systematic ointment!
Jukes-Browne, A.J., 1905. A review of the genera of the family Mytilidae. Proc Mal. Soc. London 6: 211-224.
Poel, L. van de, 1959. Faune malacologique de Hervien, troisième note (première partie). Bull. Inst. Roy. Sci. Natur. Belg. 35: 1-26.
Harry
At 09:03 PM 10/8/2009, you wrote:
I would like to thank those who provided comments and photos in response to
my post about Florida Geukensia. The references noted by Dr. Leal are
providing some difficult, but insightful reading. I guess I'm going to have
to understand cladistics. I'm still trying to determine which ancestor is
my ancestor who is not the ancestor of my sister. Appears formidable for
this old dog.
I have added everyone's observations to the presentation of G. granosissima
with some illustrations based upon Dr. Leal's comments. And, since I.
recurvum may be a nested Geukensia, I created a presentation of I. recurvum
to clear up my confusion.
http://z14.invisionfree.com/Conchologist_Forum/index.php?showtopic=1828
As always, any comments and additional photos would be very welcome. I
wonder if others have found I. recurvum to have become as scarce in Florida
as I have. Anyone found it in the Keys?????????
Marlo
merritt island, fl
Visit my website: Let's Talk Seashells
<http://s14.invisionfree.com/Conchologist_Forum/index.php?s=561483d184897208
19ac86b139d3e075&act=site>
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